Amino Acid catabolism-anabolism- Lecture 79-80

Question 1

Amino acid catabolism primarily occurs in the ______ when there are _______.

Answer 1

liver and muscle

excess amino acids in diet, during starvation, and when there is a need for gluconeogenesis (eg. log cholesterol diet)

Question 2

Name all the amino acids that can be ketogenic.

Answer 2

leucine (purely)
lysine (largely)
Phe, Tyr, Ile, Trp (can be both ketogenic and glutogenic)

Question 3

What is the C3 family?

Answer 3

amino acids that break down to pyruvate

Question 4

Which amino acids are in the C3 family?

Answer 4

Tryptophan, Alanine, Glycine, Serine, Cysteine

Question 5

What are the reactions that allow amino acids in the C3 family to break down into pyruvate?

Answer 5

Tryptophan --> Alanine
Alanine + alphaKG --> pyruvate
via GPT)
Glycine < ---- > Serine
via serine transhydroxymethylase
Serine --> pyruvate
via serine dehydratase
Cysteine --> pyruvate + Sulfate

Question 6

Which amino acids are in the C4 family?

Answer 6

Aspartate and Asparagine

Question 7

How are amino acids in the C4 family broken down?

Answer 7

Asparagine –> Aspartate + ammonia
via asparaginase
Aspartate + alphaKG –> OAA + Glut
via GOT transaminase

Question 8

Which amino acids are in the C5 family?

Answer 8

glutamate, glutamine, histidine, proline, and arginine

Question 9

How are each of the amino acids in the C5 family converted to alphaKG?

Answer 9

Glutamine –> Glutamate + NH3
via glutaminase
Histidine –> N-formimino glutamic acid (FIGLU) –> N-formino THF + glutamate
Arginine –> urea + ornithine
via arginase
ornithine –> glutamate semialdehyde
Proline –> glutamic semi-aldehyde –> Glutamate
Glutamate + NAD+ – alpha KG + NH3 + NADH
via glutamate DH

Question 10

What amino acids are in the succinyl CoA family?

Answer 10

valine, isoleucine, threonine, and methionine

Question 11

What amino acids are in the branched chain amino acid family?

Answer 11

valine, isoleucine, and leucine

Question 12

What are the steps for breaking down the branched chain amino acid family?

Answer 12

1. transamination
2. oxidative decarboxylation
   via branched chain alpha keto acid dehydrogenase with CoA, NAD, FAD, and lipoic acid cofactors
   Eventually. Valine –> propionyl CoA
   Isoleucine –> propionyl CoA
   Leucine –> acetyl CoA + acetoacetate

Question 13

What is maple syrup urine disease?

Answer 13

deficiency of the branch chain acyl CoA dehydrogenase –> accumulation of branched chain amino acids and their alpha keto acids (some of which are excreted to make urine smell like syrup)
this causes neurological disturbances, failure to thrive, coma, and death in first two years of life if untreated

Question 14

How is maple syrup urine disease treated?

Answer 14

limit branched chain fatty acids in diet

Question 15

How are phenylalanine and tyrosine broken down?

Answer 15

phenylalanine + O2 –> tyrosine + H2O
via phenylalanine hydroxylase with THB cofactor
tyrosine –> p-Hydroxyphenyl pyruvate
via tyrosine aminotransferase
p-hydroxyphenyl pyruvate + O2 + ascorbate –> homogentisate + CO2 + dehydroascorbate
homogenisate –> –> –> fumarate + acetoacetate
via homogenisate oxidase and fumarylacetoacetate hydrolase

Question 16

What is phenylketonuria (PKU)?

Answer 16

phenylalanine hydroxylase deficiency or tetrahydrobiopterin deficiency (rare) resulting in accumulation of phenylalanine which can enter pathways it doesn’t normally to produce phenylpyruvate, phenylacetate, and phenyllacetate
the accumulation of these results in neurological disturbances, impaired brain development, and death by the age of 20-30 if not well treated

Question 17

How do you treat PKU?

Answer 17

restrict phenylalanine in diet (elevate tyrosine)

Question 18

What is alkaptonuria?

Answer 18

deficiency of homogentisic acid oxidase resulting in accumulation of homogentisic acid in the blood and urine (turning it black as it oxidizes)
can result in forms of severe arthritis

Question 19

How do you treat alkaptonuria?

Answer 19

limit phenylalanine and tyrosine in diet

Question 20

How is tryptophan metabolized?

Answer 20

tryptophan –> nicotinamide component of NAD and NADP

Question 21

What is pellagra?

Answer 21

deficiency of niacin due to lack of tryptophan in diet resulting in energy imbalances, growth and brain dysfunction

Question 22

____ is essential in children/infants during development, but adults can make enough via the urea cycle.

Answer 22

Arginine